The present invention relates to a battery pack used in, for example, a lithium ion polymer secondary battery.
Recently, portable electronic apparatuses, such as a laptop personal computer, a mobile phone, and a PDA (personal digital assistant), have been spread, and, as a power source for the apparatuses, a lithium ion battery having advantages, such as high voltage, high energy density, and being lightweight, is widely used.
Further, lithium ion polymer secondary batteries that have solved a drawback of leakage of liquid, which drawback may occur when using an electrolyte in a liquid state, for example, lithium ion polymer secondary batteries using, as an electrolyte, a gelled polymer film containing a polymer impregnated with a non-aqueous electrolytic solution, or an electrolyte in a solid state have been put into practical use.
The polymer lithium ion battery has a construction of a cell including a battery element which has a positive electrode, a negative electrode, and a polymer electrolyte, wherein leads originate from the positive electrode and the negative electrode respectively. The battery element is covered with an outer covering material, such as an aluminum laminate. Further, the cell and a wiring board having a circuit portion mounted thereon are together contained in a box-form plastic molded case constituted by an upper case and lower case. An example of a lithium ion polymer secondary battery having the above described construction is provided in Japanese Patent Application Publication No. 2002-8606.